GB2030068A

GB2030068A - Manufacture of structural elements

Info

Publication number: GB2030068A
Application number: GB7923328A
Authority: GB
Original assignee: Fujitsu Services Ltd
Current assignee: Fujitsu Services Ltd
Priority date: 1978-05-03
Filing date: 1979-07-04
Publication date: 1980-04-02
Also published as: DE2917657A1; FR2424806A1; FR2424812A1; FR2424806B1; DE2917647A1; FR2424812B1; GB2030068B

Abstract

A method of constructing composite elements is described in which a surface layer 11 is constrained to form a wall of a mould 17 and plastics material is injected into the mould so as to form a substrate bonded to the surface layer. The surface layer may be constrained to a profile different from that desired in the finished element so that, after distortion of the element due to differential shrinkage of the substrate, the desired profile is obtained. Also a stabilising member may be embedded in the substrate during moulding to resist distortion of the substrate. <IMAGE>

Description

SPECIFICATION Manufacture of structural elements BACKGROUND OF THE INVENTION This invention relates to the manufacture of structural elements such as panel-like members for use in articles of furniture.

Various forms of composite structural element which includes a moulded substrate and a surface layer bonded together are described in our co-pending Patent Application No.

17405/78. These elements are suitable for use as table tops, desk panels, etc.

SUMMARY OF THE INVENTION According to the invention a process for the manufacture of a composite structural element includes the steps of constructing a mould with the surface layer of the composite element forming at least one wall of the mould and injecting plastic material into the mould to form a substrate of the desired shape within the mould and bonded to a face of the surface layer.

The use of the surface layer as an element in the mould, so that as the substrate is moulded a bond to the surface layer is also formed, provides a very simple process for forming composite element. Furthermore it eliminates any problem arising from the need to find a bonding agent which is compatible with both the substrate and the surface layer.

Also it avoids any requirement to hold the substrate and the surface layer in the required relevant positions whilst the bonding agent is setting.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a sectional view of a composite structural element.

Figure 2 shows the reverse side of such a composite structural element.

Figures 3a and 3b illustrate the dependence of curvature of the element upon the depth of the strengthening ribs.

Figure 4 shows a profiled composite structural element.

Figure 5 illustrates one part of a mould for producing a composite structural element.

Figure 6a and 6b show in section, parts of composite structural elements incorporating a stabilising member.

Figure 7a shows in section, part of a composite structural element incorporating a stabilising member as illustrated in Figure 7b.

Figure 8a shows in section, part of a composite structural element incorporating a stabilising member as illustrated in Figure 8b.

Figure 9 shows in section, part of a composite structural element in which a stabilising member is formed integrally with the substrate.

Figure 10 shows in section, part of a ribbed composite structural element in which a stabilising member is formed integrally with the ribs of the substrate and Figure 11 shows in section, part of a further construction of composite structural element.

DESCRIPTION OF PREFERRED EMBODI MENT Referring first to Figs. 1 and 2, it will be seen that the composite structural element is formed of a substrate 10 of moulded plastics material and a sheet 11 of plastic laminate which are bonded together. The substrate 10 is moulded in situ on the reverse face of the sheet 11 so that the moulding operation also effects bonding between the sheet 11 and the material forming the substrate 10. Suitable mareials from which to mould the substrate are foam resins such as rigid polyurethane, polystyrene, polypropylene, polyethylene and those marketed under the trade names of Noryl and Lexan. The laminate sheet 11 may be a laminate of melamine and sinthetic resin bonded paper PVC and aluminium or PVC and steel.The plastic material from which the substrate is formed may be subject to shrinkage after moulding with the consequence that, since the laminate sheet 11 is relatively dimensionally stable, the composite element will distort. Thus where a flat surface was formed initially the surface will become converse, as illustrated in Figs. 3a and 3b. The degree of distortion can be controlled by providing integral ribs 12 on the reverse face of the substrate 10, the degree of distortion then being dependent upon the depth 'd' of the ribs. Additional ribs 13 may also be provided.

As illustrated in Fig. 3, it will be seen that greater distortion occurs with the shallow ribs shown in Fig. 3b as compared with that which occurs with deep ribs shown in Fig. 3a, the amount of distortion being shown by the arrow between the sheet 11 and the chord 19. The provision of relatively deep ribs may not be practical due to limits upon the required maximum dimensions of the element and in addition such deep ribs require a greater quantity of material.

Referring to Fig. 4, it will be appreciated that distortion of the composite element will occur mainly in the flat area 14 of the element, since the curved portions 15, 16 of the surface sheet 11 will tend to resist distortion along the line of the curves. In order to produce a composite element having a major flat surface portion and at least one surface portion which curves out of the plate of the flat portion, a mould tool 17 (Fig. 5) is utilised in which the surface sheet 11 forms a wall of the mould and is constrained to a profile such that the part 18, which will form the flat surface in the finished composite element, is curved so as to have a concave outer surface. Parts of the sheet adjacent the curved portion 15 are constrained to the desired profile of the finished element.The curvature to which the sheet is constrained is so chosen that with the rib structure of the substrate with is to be moulded thereon and taking into account the shrinkage of the substrate which will occur after moulding, the composite structure will assume a profile after such shrinkage has taken place which is the desired profile of the composite element.

While in the above method, only the part of the sheet forming the major flat surface has been described as being constrained into a concave profile, other portions which it is determined will be distorted by shrinkage of the substrate may be constrained to a concave profile. For example the rounded edge portion 15 may be so constrained. The curvature to which the sheet is constrained in the mould may be different for different parts of the sheet and may be different in different directions.

Alternatively instead of moulding the substrate in such manner that after distortion thereof the surface acquires the desired profile as described above, distortion of the element may be resisted by incorporation of a stabilising element in the substrate, at least in that part which corresponds to the flat area. The stabilising element may be constructed in a number of ways as illustrated in Figs. 6 to 11 In Fig. 6a, the substrate 10 is of slab-like construction and the stabilising member consists of a mesh consisting of a set of wires or rods 17 extending perpendicular to a similar set of wires or rods 18. This mesh is located within the thickness of the substrate adjacent the reverse face thereof remote from the surface layer 11. Fig. 6b shows a construction using the same mesh of wires located so that the wires each extend along the free ends of the ribs 12.

Fig. 7a shows a construction of composite element having ribs 12 in which a stabilising member shown in Fig. 7b is incorporated. The stabilising member consists of a plurality of interlocking strips 19 arranged to extend within the thickness of the ribs. The strips 19 preferably are provided with apertures 20 to ensure that a good bond is formed between the material used for moulding the substrate and the strips.

Fig. 8a shows a construction of composite element in which the substrate of slab-like construction and the stabilising element consists of a plate 12 having a plurality of apertures 22 therein. The plate 21 is located within the substrate 10 adjacent the reverse face thereof remote from the surface layer 11.

Instead of providing a separate stabilising member as described in the embodiment in which the member is embedded in the substrate, the material of the substrate itself may be differentially modified in order to produce an integrally formed stabilising member. The major part of the thickness of the substrate is of foamed plastic material 23 whereas at the faces of the substrate skins 24, 25 are formed which are not foamed. The mould face adjacent the surface layer 11 is heated to a relatively high temperature so that a relatively thin skin 24 is formed adjacent the layer 11.

The stabilising member is formed of a relatively thicker skin 25 on the substrate 10 remote from the surface layer 11. This is accomplished by the mould surface being relatively cold so as to cause earlier chilling of the plastic adjacent that mould surface.

The same principle may be applied to a ribbed composite element shown in Fig. 10 in which at least the free ends 26 of the ribs 12 are chilled during moulding while the inner part of the substrate and the roots of the ribs 12 are of foamed material 23.

If desired additional stabilising may be provided by a second surface layer 27 (Fig. 11) bonded to the reverse face of the substrate 10 so that distortion of the element is resisted not only by the non-foamed skin 25 but also by the second layer 27.

The stabilising member may be of metal or plastic of such composition that it is capable of resisting shrinkage of the foamed plastic material of which the substrate is formed.

If desired a combination of the methods may be used, a stabilising member being provided and the composite structural element being moulded so as to have parts of the surface layer more convex than desired for the final element whereby a degree of shrinkage can take place and thereby provide an element having a surface layer presenting a flat or other desired profiled surface.

Claims

1. A process for the manufacture of a composite structural element includes the steps of constructing a mould in which a surface layer of the element forms at least one wall of the mould and injecting plastics material into the mould to form a substrate of desired shape within the mould and bonded to a face the surface layer.

2. A process as claimed in claim 1 including the step of constraining the surface layer to conform to a desired profile for the composite structural element.

3. A process as claimed in claim 1 including the step of constraining the surface layer to conform to a profile different from a desired profile of the composite structural element so that after distortion of the substrate due to differential shrinkage thereof following tne moulding step the composite structural element acquires the desired profile.

4. A process as claimed in any preceding claim including the step of positioning a stabilising element in the mould spaced from the surface layer prior to the step of injecting plastics material into the mould so that the stabilising element is embedded in the moulded substrate and is effective to resist distortion of the substrate.

5. A process as claimed in any preceding claim including the step of differentially modifying the material forming the substrate so that material remote from the surface layer is more resistant to shrinkage than material adjacent the surface layer.

6. A process as claimed in any preceding claim in which the mould is shaped to form ribs on the substrate projecting away from the surface layer.

7. A process as claimed in claim 6 including the step of positioning a stabilising element in the mould spaced from the surface layer so that the stabilising element extends within the ribs of the moulded substrate.

8. A process as claimed in claim 6 or 7 including the step of differentially modifying the material forming the substrate so that material in the ribs is more resistant to shrinkage than material adjacent the surface layer.

9. A process for the manufacture of a composite structured element substantially as hereinbefore described with reference to Figs.

4 and 5 of the accompanying drawings.

10. A process for the manufacture of a composite structured element substantially as hereinbefore described with reference to Figs.

6a, 6b, 7a and 7b or 8a and 8b, of the accompanying drawings.

11. A process for the manufacture of a composite structured element substantially as hereinbefore described with reference to Figs.

9, 10 or 11 of the accompanying drawings.